This is a continuation-in-part of applications Ser. No. 76,098 filed Jul. 21, 1987 now U.S. Pat. No. 4,927,736 and Ser. No. 915,342 filed Oct. 2, 1986 now abandoned.
The present invention relates to negative-acting photoresist compositions based upon soluble hydroxy-containing resin binder materials, which compositions are developable by means of conventional alkaline developer solutions, provide high resolution at relatively short exposure times and most preferably are thermally stable at relatively high temperatures.
Applications Ser. No. 76,098 and Ser. No. 915,342 relate to the production of novel soluble hydroxy polyimide and hydroxy polyamide resin binder materials and their use in making base-developable positive acting photoresists for high temperature applications. The present invention relates to the use of the soluble hydroxy polyimide and hydroxy polyamide resin binder precursors disclosed in said applications to produce photoresist compositions which are negative acting and base developable.
Generally, positive-acting photoresist compositions have been preferred. They are soluble in common organic solvents and can be developed in conventional alkaline developers. This solubility is preserved in the positive photoresist process in which the exposed, uncoupled areas of the photoresist coating retain their original solubility while the unexposed masked areas are coupled with the azo photoinitiator to a condition in which they are rendered insoluble in alkaline developers. Reference is made to U.S. Pat. Nos. 4,093,461; 4,339,521 and 4,395,482 for their disclosure of such positive-acting photoresist compositions.
It is desirable to provide negative acting photoresist compositions which are temperature stable and provide high resolution at low exposure times, in the same manner as known positive acting photoresist compositions, and are also developable by means of conventional alkaline developers. High temperature-resistant negative-acting photoresist compositions are known but such compositions generally are not soluble in or developable by conventional alkaline developers, and therefore require the use of organic solvents such as dimethyl formamide and butyrolactone as developers. Reference is made to U.S. Pat. Nos. 3,957,512; 4,045,223 and Re. 30,186 for their disclosure of such negative-acting photoresist compositions.
In the industrial application of positive and negative resists, the polymeric component and the radiation sensitizer are dissolved in an organic solvent or mixture of solvents and applied as a thin film or coating to a substrate suitable for the desired application.
The polymeric component of these resist formulations is desirably soluble in aqueous alkaline solutions, but the sensitizer acts as a dissolution rate inhibitor with respect to the polymer. Upon exposure of selected areas of the coated substrate to actinic radiation, the sensitizer undergoes a radiation induced structural transformation and the exposed areas of the coating generally are rendered more soluble than the unexposed areas. This difference in solubility rates normally causes the exposed areas of the resist coating to be dissolved when the substrate is immersed in alkaline developing solution leaving the unexposed areas substantially intact, thus producing a positive relief pattern on the substrate.
In most applications, the exposed and developed substrate will be subjected to treatment by a substrate-etchant solution. The resist coating protects the coated areas of the substrate from the etchant and thus the etchant is only able to etch the uncoated areas of the substrate, which in the case of a positive resist, corresponds to the areas that were exposed to actinic radiation, and in the case of a negative resist, corresponds to the areas that were masked and not exposed to actinic radiation. Thus, an etched pattern can be created on the substrate which is a positive or a negative of the pattern of the mask, stencil, template, etc., that was used to create selective exposure patterns on the coated substrate prior to development.
The relief pattern of resist on the substrate produced by the methods described above is useful for various applications including, for example, as an exposure mask or a pattern such as is employed in the manufacture of miniaturized integrated electronic components or the manufacture of a printing plate.
The properties of a resist composition which are important in commercial practice include the solubility of the resist in the application solvent, the photospeed of the resist, development contrast, environmentally acceptable developer solubility, resist resolution, resist adhesion, dimensional stability at elevated temperature and abrasion resistance.
Photospeed is important for a resist, particularly in applications where a number of exposures are needed, for example, in generating multiple patterns by a repeated process, or where light of reduced intensity is employed such as in projection exposure techniques where the light is passed through a series of lenses and mono-chromatic filters. Thus, high, controlled photospeed is particularly important for a resist composition employed in processes where a number of multiple exposures must be made to produce a mask or series of circuit patterns on a substrate. Control of the photospeed is extremely important in order to produce high resolution relief patterns in microcircuitry; e.g., a photospeed too high can result in narrowing the processing conditions.
Resist resolution refers to the capability of a resist system to reproduce the smallest equally spaced line pairs and intervening spaces of a mask which is utilized during exposure with a high degree of image edge acuity in the developed exposed spaces. In many industrial applications, particularly in the manufacture of miniaturized electronic components, a resist is required to provide a high degree of resolution for very small line and space widths (on the order of a micron or so).
The ability of a resist to reproduce very small dimensions, on the order of a micron or so, is extremely important in the production of large scale integrated circuits on silicon chips and similar components. Circuit density on such a chip can be increased, assuming photolithography techniques are utilized, by increasing the resolution capabilities of the resist.
Various attempts have been made in the prior art to produce high temperature positive resists possessing the above desired properties. For example, U.S. Pat. No. 4,093,461 discloses a heat resistant, positive resistant composition comprising a quinone or naphthoquinone diazide and the polycondensation product of an aromatic dianhydride (pryomellitic anhydride) and an aromatic diamine (4,4,-diaminodiphenylether). The properties of the positive resist of the patent are discussed in U.S. Pat. No. 4,395,482 (column 1, lines 46-64). There it is pointed out that the positive resist composition of U.S. Pat. No. 4,093,461 has limited storage life, insufficient stability to alkaline etching solutions and relatively small differences in solubility between the exposed and unexposed portion of the resist.
The use of imagable polyimide and polyamide resist systems has been limited by the lack of photospeed (slow photospeed), excessive volume contraction and by shelf life problems. The exceptional dielectric and high temperature resistance properties of polyimides make them particularly useful in the semiconductor industry. They can be used, for example, as dielectric layers, alpha particle barriers in memory devices, ion implantation masks and passivation layers. The goal of numerous development programs has been the development of a simple, reliable and cost effective radiation sensitive polyimide system that could be used with common photolithographic equipment and processes. This was the goal of by the work of R. Rubner et al. of Siemens Co. (R. Rubner, H. Ahne, E. Kuhn, G. Kolodziej; Phot. Sci. 4 Eng. 23(5), 303-309 (1979). H. Ahne, H. Kruger, E. Pammer and R. Rubner, "Polyimide Synthesis, Characterization and Application", K. L. Mittal ed., Vol. 2, 905-918, Plenum Press (1984). The basic systems in these publications consist of polyamic acid polymer bearing photoreactive side groups. To date, however, materials based on this chemistry have been plagued by poor shelf life, extraordinarily low photospeed and excessive post-development/post-cure structure contraction. Although materials based on this chemistry have yielded high resolution structures, they required exposures of ten minutes or longer. Shelf life was also notoriously short, particularly in highly concentrated solutions required for thick film applications and contraction of original structures upon cure was as much as 60 percent.
The present invention uses the novel fluorinated hydroxy polyimides and fluorinated hydroxy polyamides of the parent applications as a binder material to provide negative photoresist compositions e.g., an alkali soluble hydroxy polyimide or hydroxy polyamide together with a photopolymerizable multifunctional acrylate and photoinitiator to provide high temperature negative photoresist protective coatings for producing negative patterns with excellent resolution and adhesion properties.